The Maryland Transit Administration is recording conversations between bus drivers and passengers in what critics are calling a privacy violation.

The Baltimore Sun reported that audio recording began on 10 buses in Baltimore this week. The agency plans to expand the program to half its fleet by next summer.

MTA buses already have video cameras. The state attorney general's office said the addition of audio doesn't violate Maryland's wiretapping law. Signs on the buses tell riders they are being recorded.

But the American Civil Liberties Union said bus riders shouldn't have to sacrifice their privacy rights. Montgomery County Sen. Brian Frosh, D-District 16, said the General Assembly will likely set standards for oversight and accountability.